Cross-reference is hereby made to copending and commonly assigned U.S. patent application Ser. No. 09/363,782 filed Jul. 29, 1999 and entitled Closed Loop Photoreceptor Belt Tensioner by Daniel W. Costanza et al.
The present invention relates generally to an electrostatographic printing machine, and more particularly, concerns improving color registration of images on a flexible photoreceptor within such a machine.
Flexible electrostatographic imaging members are well known in the art. Typical electrostatographic imaging members include, for example, photoreceptors for electrophotographic imaging systems and electroreceptors such as ionographic imaging members for electrographic imaging systems. These imaging members generally comprise at least a supporting substrate layer and at least one imaging layer comprising thermoplastic polymer matrix material. The "imaging layer" as employed herein is defined as the dielectric imaging layer of an electroreceptor or the photoconductive imaging layer of a photoreceptor. In a photoreceptor, the photoconductive imaging layer may comprise only a single photoconductive layer or a plurality of layers such as a combination of a charge-generating layer and a charge transport layer.
Although the discussions hereinafter focus only on flexible electrophotographic imaging members, nonetheless the problems encountered therewith are equally applicable to electrographic imaging members.
Generally, in the art of electrophotography, the process of electrophotographic copying is initiated by exposing a light image of an original document onto a substantially uniformly charged photoreceptive member. Exposing the charged photoreceptive member to a light image discharges a photoconductive surface thereon in areas corresponding to non-image areas in the original document while maintaining the charge in image areas, thereby creating an electrostatic latent image of the original document on the photoreceptive member. This latent image is subsequently developed into a visible image by depositing charged developing material onto the photoreceptive member surface such that the developing material is attracted to the charged image areas on the photoconductive surface. Thereafter, the developing material is transferred from the photoreceptive member to a receiving copy sheet or to some other image support substrate, to create an image, which may be permanently affixed to the image support substrate, thereby providing an electrophotographic reproduction of the original document. In a final step in the process, the photoconductive surface of the photoreceptive member is cleaned with a cleaning device, such as elastomeric cleaning blade, to remove any residual developing material, which may be remaining on the surface thereof in preparation for successive imaging cycles.
The electrostatographic copying process described hereinabove, for electrophotographic imaging, is well known and is commonly used for light lens copying of an original document. Analogous processes also exist in other electrostatographic printing applications such as, for example, digital laser printing where a latent image is formed on the photoconductive surface via a modulated laser beam, or ionographic printing and reproduction where charge is deposited on a charge retentive surface in response to electronically generated or stored images. One of the drawbacks to the above-described process utilizing a flexible imaging member belt is that the belt, a photoreceptor belt in particular, stretches during repeated use. This is due to the machine belt module design employing a number of backer bars and small diameter belt support rollers to support the photoreceptor belt for movement during electrophotographic image processing cycles and keeping the belt under tension at all times. The constant tension on the photoreceptor belt, the positioning of the backing bars, and the positioning of the small diameter rollers causes substantial belt fatigue through bending stress/strain build-up in the charge transport layer, promoting the onset development of premature charge transport layer stretching and cracking as a result of repetitions of the photoreceptor belt flexing over the small diameter belt support rollers and backer bars during machine cyclic photoreceptor belt function.
Stretching of the photoreceptor is considered to be a major mechanical failure since misregistration of color images during image-on-image printing manifests itself into copy print out defects.
Therefore there is a need for a photoreceptor belt tensioning system that achieves superior color registration while reducing belt tension during belt steering actuations.